The operation of vehicles is prohibited if:

Explanation

Both the fitting of tyres of different construction on the same axle and damage to the engine's fuel supply system.

Both items appear separately on the list of prohibiting defects, so the comprehensive answer is correct.

Combining tyres of different construction on one axle — radial on one side and bias-ply on the other, say — means the two wheels of an axle work with different sidewall stiffness and different behaviour under load. The result does not show in gentle driving, but under hard braking or in a sharp bend the grip on the two sides becomes unequal and the car pulls to one side or its rear slides. The same logic applies to large differences in wear, size or tread type (winter and summer on one axle).

Damage to the fuel supply system is a matter of fire. The smallest leak of petrol or diesel onto a hot manifold or near an electrical spark can start a vehicle fire; a fire that spreads rapidly in the enclosed engine bay and, in a collision, takes away the occupants' chance of getting out. That is why a fuel leak is never "tolerable as far as the workshop".

Exam note: any option referring to a fuel leak, a brake fluid leak, or a difference between the tyres of one axle is almost always on the prohibition list.

• Correct but incomplete; tyres of different construction on one axle really are prohibited, but this option sets aside the damage to the fuel supply system. • Damage to the fuel supply system is independently a ground for prohibition too; choosing it alone leaves the answer incomplete.

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